What is the difference between typeof and instanceof

The difference between typeof and instanceof is: the return value of typeof is a string, used to describe the data type of the variable; the return value of instanceof is a Boolean value, used to determine whether a variable belongs to an instance of an object .

Compare typeof and instanceof

Same points:

typeof and instanceof in JavaScript are often used to determine whether a variable is empty , or what type it is.

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Differences:

typeof:

1. The return value is one String used to describe the data type of the variable.

2. Typeof generally can only return the following results: number, boolean, string, function, object, undefined.

 if (typeof a != "undefined") {
   console.log("ok");

 } eles {
    console.log("not ok");
}
//下面的代码是错误的
// if (a) //因为如果 a 不存在（ 未声明） 则会出错。
// if (a) {
//     console.log("ok");

// } else {
//     console.log('cc');

// }

Using typeof for special objects such as Array and Null will always return object. This is the limitation of typeof.

instanceof:

1. The return value is a Boolean value

2. Instanceof is used to determine whether a variable belongs to an instance of an object.

// var a = new Array();
// alert(a instanceof Array); // true
// alert(a instanceof Object) // true
//如上， 会返回 true， 同时 alert(a instanceof Object) 也会返回 true;
// 这是因为 Array 是 object 的子类。
// alert(b instanceof Array) // b is not defined

// function Test() {};
// var a = new test();
// alert(a instanceof test) // true

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